Chemical oxygen (pyrotechnic) gas generators have been developed and used already for long periods. Self-controlled, continuously ready to operate for many years without any verification tests, easy activation from low-power electric sources, small size, safe, a rather high yield of oxygen on a per-unit volume and unit mass and a number of other advantages make them irreplaceable in case of emergencies and in accidents. They are used and applied, for instance, for the emergency supply of oxygen to the passengers in aircraft in case of cabin depressurization, in submarines if the other emergency oxygen supply systems fail, in space stations in case of emergency if the basic oxygen supply systems fail, and in many other conceivable emergency cases. A typical example of the use of oxygen generators on-board aircraft is presented in U.S. Pat. No. 4,840,171.
An operational application is the supply of oxygen for firefighters. Other cases to provide oxygen to satisfy operational requirements are e.g. for divers, or for driving rocket engines on-board spacecraft. In all these cases oxygen has to be provided independently of the ambient or surroundings.
In general, oxygen may be provided from oxygen stored in bottles or from oxygen generators. The latter in many cases are lighter and less voluminous for the same amount of oxygen than bottles. Chemical oxygen generators are the subject of this invention. Chemical oxygen generators are well known to those versed in the art. As a rule, chemical compounds, which release oxygen during thermal decomposition, are used in chemical oxygen generators. The following compounds are commonly used:                Alkali metal chlorates and alkali metal perchlorates, especially Lithium perchlorate (LiClO4), Lithium chlorate (LiClO3), Sodium perchlorate (NaClO4), Sodium chlorate (NaClO3), Potassium perchlorate (KClO4) or Potassium chlorate (KClO3);        Peroxides, especially Sodium peroxide (Na2O2) and Potassium peroxide (K2O2)        Superoxides, especially Potassium superoxide (KO2) and Sodium superoxide (NaO2)        
Special additives are used in small amounts to assure self-sustained decomposition (combustion) while releasing oxygen. These additives also control the reaction rate, and form a heat resistant slag with a high-melting point and scavenge harmful gases (i.e. impurities, e.g. chlorine, its compounds and others) that may be released by side reactions.
Typical Examples of These Additives Are:
                Metals: Aluminum, Magnesium, Zinc, Manganese, Molybdenum, Cobalt, Nickel, and in particular Iron;        Cobalt oxides (Co2O3 and Co3O4), Chromium oxide (Cr2O3), Copper oxide (CuO), Iron oxide (Fe2O3), Zinc oxide (ZnO), Manganese oxide (MnO), Manganese dioxide (MnO2), Magnesium oxide, (MgO), Silicium dioxide (SiO2)        Alkali peroxides, specifically Sodium peroxide (Na2O2), Potassium peroxide (K2O2), Barium peroxide (BaO2)        Alkali super-oxides, specifically Sodium superoxide (NaO2) and Potassium superoxide (KO2)        
U.S. Pat. No. 6,126,854 mentions a number of combinations and specifically mentions magnesium oxide to control the decomposition reaction, suppress chlorine formation, improve the rheology and facilitate the mixing. One reason for improving the rheology and the mixing, is the way in which the oxygen candle according to U.S. Pat. No. 6,126,854 has been made. The present invention avoids several of these difficulties. U.S. Pat. No. 3,868,225 discusses another oxygen generator (or oxygen candle). Materials, like asbestos, which are presently considered a health hazard, are used in this patent to obtain oxygen of breathing quality. The cool oxygen gas generator which is subject of this invention does not use asbestos.
U.S. Pat. Nos. 5,336,470 and 5,322,669 discuss means to control the mass flow rate of the oxygen. This is done by introducing barriers of various shapes. These barriers on one hand create a specific path for the decomposition front, but also specifically serve to absorb heat from the decomposition reaction. This is certainly required if the chemical oxygen generator has to provide oxygen for breathing purposes. For example, the decomposition of sodium chlorate is according to the reaction:2NaClO3→2NaCl+3O2+101 kJ
To maintain the decomposition reaction, fuel like iron (Fe) is added to the mixture. The decomposition temperature of the mixture is in the order of 1500 K. In a classical chemical oxygen generator heat is absorbed by the additives and the housing, but insulation material is required to prevent the outside of the housing becoming too hot and additional heat sinks to cool the oxygen to acceptable temperatures. U.S. Pat. No. 3,868,225 uses glass fiber as insulating material and a double wall through which coolant air may pass. Nevertheless, oxygen temperatures of 370° C. (700° F.) are reported. It is obvious that if the oxygen is to be used directly for breathing, it must be cooled down further, which usually is done by large heat capacity filters. These serve the purpose of filtering the oxygen gas from particulate material and polluting chemicals, if present, but especially to cool the oxygen. Therefore, these filters are much larger and heavier than would be the case if the only purpose was to filter and cleanse the oxygen. In fact, the filters are counterproductive for mass and volume reduction. The importance of low mass is specifically stressed in U.S. Pat. No. 6,007,736.
The present invention circumvents the problems of the prior art, by making use of a technology that has been described in the Russian patent 2108282 and the International patent application PCT/NL00/00696, publication Number WO 0123327. Here the hot decomposition gas is passed through the not reacted material, thereby raising the temperature of the virgin material and cooling the produced gas. However, to accomplish this it is necessary to make a porous charge that remains integer during the decomposition when oxygen is released. If that were not the case, particulate material might clog the porous charge and functioning of the gas generator would be impaired. U.S. Pat. No. 4,981,655 teaches a chemical oxygen generator where also the hot oxygen passes through the virgin material. However, this virgin material consists of loose pellets held together and compressed by a spring load. The pellets themselves are specially manufactured and consist of a cylindrical center body and two hemispherical end caps. The cylindrical part can even be of a different chemical composition than the hemispherical end caps. Although the dimensions of the pellets are not given in U.S. Pat. No. 4,981,655, it can be inferred from the drawings that they are of macroscopic dimensions; therefore the specific surface area for contact with the hot oxygen is much smaller than the specific surface of the porous virgin material that is subject of the present invention.